Smoking and Metabolic Injury to the Myocardium

To the Editor:—  In his interesting editorial in The Journal (186:509 [Nov 2] 1963), Dr. William Dock, referring to the analogy between the well-known adrenergic effects of nicotine and of physical exertion on the heart, suggests that "Possibly... a cigarette may substitute for exercise, which is so often praised as protection against atherosclerosis." This hypothesis may give unwarranted comfort and encouragement to sedentary smokers.Nicotine and physical exertion produce identical cardiac effects by acutely liberating sympathogenic norepinephrine and epinephrine. These catechol amines increase myocardial oxygen consumption, thus causing hypoxia in whichever area of the heart muscle the normal compensatory dilatability of coronary vessels is impaired by sclerosis.However, the state of being physically trained, in contrast to the individual act of acute exertion, is characterized by a sustained (probably hypothalamus-mediated) lowering of the cardiac sympathetic tone, to the advantage of myocardial oxygen economy. Habitual smoking, on the other hand,